1. Field of the Invention
The present invention relates to a glass ceramic board formed by simultaneously burning a glass ceramic insulating material and a silver-type conductive material at a predetermined burning temperature.
2. Description of the Related Art
There have recently been great demands for decreasing the size and cost of electronic apparatus such as a portable telephone terminal, a computer or the like, and improving the function and reliability thereof, and electronic parts such as semiconductor IC, etc. have significantly developed to high density integration, and high speed operation with these demands. Accordingly, conductive materials used as a substrate material on which electronic parts are mounted are required to have higher characteristics than alumina substrate materials and tungsten conductive materials.
Particularly, alumina has a high dielectric constant and thus has a problem of delay of signal propagation in a wiring pattern. Alumina also has a large difference in thermal expansion coefficient from silicon or the like and thus causes deterioration in reliability due to thermal cycling. Furthermore, since alumina has a high sintering temperature, a high-melting-point metal such as tungsten, molybdenum or the like must be used as the conductive material. However, these high-melting-point metals have high resistivity and thus have the problem of causing difficulties in high-density wiring.
With refinement of a conductor (wiring) pattern and increases in signal frequency, an attempt is made to use a glass ceramic multilayer circuit board comprising a glass ceramic material burnable at 1000xc2x0 C. or less, and a low-melting-point metal conductive material having low resistivity, such as copper, silver, gold, platinum, silver-palladium alloy, or the like.
Of these conductive materials, gold and platinum are burnable in the air, but the material cost thereof is high. Copper is required to be burned under strict control in a reducing atmosphere, and thus has the problem of high burning cost, etc. Therefore, silver-type conductive material are widely used, as they have a relatively low material cost and are burnable in air and thus have low burning cost.
However, silver-type conductive materials such as silver, silver-palladium alloys and the like, readily diffuse as compared with other conductor materials, and thus cause a short circuit between wirings due to contact between the diffused silver particles, thereby making the reliability of the obtained wiring board unstable. In addition, the diffused silver particles produce a silver colloid, and thus cause discoloration of the board due to the silver colloid, deteriorating the quality of the board. Particularly, in a glass ceramic multilayer circuit board, silver is readily diffused into the glass component, and thus the suppression of silver diffusion is a great problem.
To overcome the above described problems, preferred embodiment of the present invention provide a glass ceramic board with high reliability and high quality, in which silver diffusion of a silver-type conductive material can be suppressed.
One preferred embodiment of the present invention provides a glass ceramic board formed by simultaneously burning a glass ceramic insulating material, and a silver-type conductive material at a predetermined burning temperature, wherein a metal stably or metastably present at room temperature and forming an oxide at the burning temperature is added to the glass ceramic insulating material.
In the above described glass ceramic board, the metal may be at least one selected from the group consisting of aluminum, silicon, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc and gallium.
In the above described glass ceramic board, the metal may be copper.
In the above described glass ceramic board, the amount of the metal added may be about 3% by weight or less based on the glass ceramic insulating material.
In the above described glass ceramic board, the glass component of the glass ceramic insulating material may be at least one selected from the group silicate glass, borosilicate glass and CaOxe2x80x94SiO2xe2x80x94Al2O3xe2x80x94B2O3 glass.
In the above described glass ceramic board, the ceramic component of the glass ceramic insulating material may be at least one selected from the group consisting of alumina, silica, zirconia, forsterite, anorthite and wollastonite.
In the above described glass ceramic board, the weight ratio of the glass component to the ceramic component in the glass ceramic insulating material may be about 10:90 to 100:0.
The above described glass ceramic board may comprise a multi-layer board comprising a lamination of a glass ceramic insulating layer and a silver-type conductive layer, with the silver-type conductive material being used for surface conductor patterns and/or inner conductor patterns.
In the above described glass ceramic board, a metal which is stably or metastably present at room temperature and which forms an oxide at a burning temperature of 700 to 960xc2x0 C., i.e. lower than the melting point of silver, is added to the glass ceramic insulating material. Therefore, for example, at the burning temperature in a non-reducing atmosphere such as the air or the like, oxidation and diffusion of the silver-type conductive material are suppressed, thereby obtaining a glass ceramic board having high reliability and high quality. This is due to the fact that the metal is more easily oxidized than the silver-type conductive material which forms conductor patterns, and functions as a reductant for the silver-type conductive material.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.